Processes for the utilization of exhausted liquors



Oct. 23, 1956 G. mom

PROCESSES FOR THE UTILIZATION OF EXHAUSTED LIQUOR-S Filed Jan. 25, 1952 Int 017w United States Patent PROCESSES FOR THE UTILIZATION OF EXHAUSTED. LIQUORS Giacinto-Diotti, Milan, Italy; assignorof'one-lialf' fo shia Viscosa, Societa Nazionale 'Indilstri'a Applicazioni Viscosa, Societa per. Azioni,.Milan;.Italy,.an Italian jointstock company Application January2'3', 1952, Srial-No:-267,739" Claims'priority, application ItalyJanuaryZS, 1951 1 Claim. (Cl. 260347.9)

Aiprocedure forthe utilization of liquors that are: discharged after a charge of wood has" been: digested ito ob?- tain cellulose therefrom; and which are termed: exhausted liquors." or in the interest. of brevityliquors,i"has been specified in applicants copending patent application; Serial No. 267,740, filedr on January23,.1 9i52.

According. to theco-pending application,- there'ca-n; be carried out a process for'the production: of; furfura'li or other cyclized heterocycles. in a thermal-compression evaporator using exhausted liquors having'a relatively high pentose contentas for example: those' which are discharged. after a charge of deciduouswoodshasbeen digested with bisulphite'-the pentoses. being converted into furfural' thereby heating the. liquor'upto sufficiently high temperature,.the furfural being then removed from liquor. in any convenientway; as hy.- the well: known. dis? tillation' systems.

According to the above said copending patent application, the liquor may be submitted to a) given. concentras tion, before the pentoses are" converted into furfurali The mother liquor, after the furfural has been removed therefrom may be disposed of as a low grade fuel in a known manner, provided it is concentrat'ed 'upto a sulficient solids content; which may conveniently be about 50%. As is readily appreciated the economy of. this process is a function of the ratio of the heat obtained by burning the concentrated liquor, to the heat required to concentrate it. Obviously, the solid matter: contents must be selected in such a manner asrtohaversaid-rratio brought up to highest possible value. Moreover, the manner in which-the concentrationis elfected, particularly with respect to. efliciency of 'concentratorsgis: also ofi consequence. Due to economic reasons,.sarneconcentrators are practically always of'the' thermocompression orrmultiacting type, for a single stage or" thermocompression. con:- centration is to be considered as equivalent to many stages of a conventional concentrator.

This invention relates to an improvement in the procedure in the above referred copending patent application, and is intended to allow a thorough utilization of liquor with the lowest consumption both of reagents and of heat. Such an end can be attained by utilizing the liquor both as a furfural source and as a low grade fuel, and by following a mode of operation such that the heat input will serve at the same time for both of said purposes in conserving the total heat requirement and in returning the fuel to the process as a source of heat. Thus the economy of operational cycle is remarkably improved, and a solution with a relatively high furfural content is obtained from the exhausted liquor wherein the heat requirement is remarkably low.

According to the present invention, the liquor is submitted in a first stage to a concentration amounting only to a part of the final value required for its utilization as a low grade fuel. Then, the pentoses are converted into furfural in the manner disclosed in the application above referred to, whereupon the preliminary concentrated liquor, together with its furfural contents, is brought to a final; concentration value, in which the content is obtained of solidmattera's required for its utilization as low grade fuel; The furfural. formed is removed with the vapours'evolved during this final concentration stage, and is collected, under: recovery of vaporisation heat, in the form of a. condensed liquid, having a relatively high furfural content, and: that can. be distilled in. a very economical manner;

To attainithe best" operational efiiciency, the heating of theliquor, required to cause the conversion of'pentoses, can 'be efiected at'least partly in counterflow, whereby the liquorv coming from preliminary concentration, is-heated by. the inflolwing. liquor wherein the furfural has already beenformed, and this is cooled before it isbrought to its final: concentration. The heating can. be conveniently effectediinatwosteps-eachstep under the. most suitable pressure. The" first: step (up to av temperature. slightly lower: thanthe'maxirnumvalue required) is carried out inan heat exchanger, atthe expense of the heatgiven up by the liquor wherein: the furfural has already formed; in the second step (term at the over-heating step) the liquor is brought to the maximum temperature by any suitable means. Thus, the costs involved in the heating operationsare those springing from heat' losses from superheaterand' heatexchanger, which'losses may be minimizedby means that are'wellknown. However, the counterfiowheating step is not essential; in view ofthe wide rangeof thermal and ther-modynamic cycles which can be" carriedout within the limits of'the presentinvention. lirthepresent invention the conversionof pentoses by means ofthe heating is combinedwith the concentration of liquor to convert thislatt'er into a low grade fuel, in such a manner that aportion of heat inputwhich would be at any rate required forsucha cyclei's-utilized also to separate from liquor a solution showing a' relatively high furfural content, which can" be then economically submitted to afractional distillation.

The degree of preliminary concentration of liquor may be varied" according to the liquor' composition, the con centrator' type and also-to economical factors; In the usual cases, such a concentration is preferably driven up to attainment ofa solids content nearly double that of the" original one; however, this is not essential. From an. economical viewpointthere is in each case a concentration optimum, and by departing therefrom, the gains that can be drawn from the procedure are reduced; but not nullified at'least' up to a certain point. Atany rate, itimustbe remembered" that on'the one handit is advanta'geous that-*the'heating' beefiected on a highlyconcentrated liquor, while on the other han'dan' amount ofwater sufiicient to keep the furfural in solution must be present in the liquor which is delivered for final concentration.

Two embodiment forms of the invention are describedfor the purpose 'of illustration only-in the hereinafter stated examples, taken with the accompanying drawing, in which the Fig. 1 shows diagrammatically the equipment according to Example I, and Fig. 2 shows diagrammatically the equipment according to Example II. It is to be understood that the description is not definitive of the limits of the present invention, for it may be carried into practice by persons skilled in the art in equivalent manners and modifications as are well-known.

Example I The bisulfite liquor in which the digestion of an eucalyptus wood charge has been effected, and that at the end of cooking shows a dry solids content of l60l70 grams per literof which 14-16 grams are pentosesis discharged at a temperature of 110 C. from digester 1 into the tank 2 wherefrom by means of pump 3 it is pumped into the last three elements 4-56 of a quadruple effect concentrator, wherein a concentration is Obtained up to a dry solids content of 320-340 grams per liter (of which 32 grams are pentoses) will take place. Then the liquor, as discharged from element 6 of concentrator, is sent by the pump 7, under a pressure of 15-16 kg./sq. cm., to superheater 8, wherein it is heated up to a temperature of 170-190 C. by means of superheated steam. The capacity of said superheater 8 must be such as to allow the liquor to stay therein for a time of 10-20 minutes. As a consequence of the high temperature attained in the superheater, the pentoses contents of liquor are converted into furfural and therefore the liquor, as discharged from superheater 8, will contain 10-12 grams of furfural per liter. Such a liquor is then sent to first element 9 of quadruple eifect concentrator, wherein it is ultimately concentrated until a dry matter contents of 520-560 grams per liter is attained. The whole of liquor furfural contents is removed off together with the vapour evolved from element 9 of quadruple action concentrator, and that is utilized to heat all other elements of same concentrator, whereby a condensed liquid showing a furfural contents of 5-6 percent is discharged from element 6 of concentrator, and then sent to distillation column 10. The concentrated liquor that is discharged from element 9 of quadruple action concentrator, can be directly utilized as a low grade fuel.

Example 11 The bisu'lfite liquor in which the digestion of a charge of common cane (Ar-undo donax) has been effected, and that at the end of cooking shows a dry matter contents of 130-140 grams per liter (whereof 20-25 grams of pentose) is discharged at a temperature of 100-1l0 C. from digester 1 into the tank 2, whereupon it is sent by means of pump 3 to thermocompression concentrator 4 in which it is concentrated up to a dry matter contents of 260-280 grams per liter (whereof 40-50 grams are pentoses). The concentrated liquor, discharged from concentrator 4, is sent by the pump 5, under a pressure of 15-16 kg./ sq. cm., to heat exchanger 6, where it is brought to a temperature of l50-160 C. at the expenses of the heat given up by the liquor coming from superheater 7, and that flows in countercurrent through the heat eX- changer. Then the liquor is passed from heat exchanger 6 to superheater 7, wherein it is heated from 150-160 C. up to 170-l90 C. by means of superheated steam. The capacity of said superheater must be such as to allow the liquor to stay therein for a time of -20 minutes before it is sent back to heat exchanger 6 where, as aforestated, it will give up a part of its heat to incoming liquor, being thus cooled from 170-190 C. down to 120-130 C. Owing to high temperature attained in the superheater, all pentoses present in the liquor are converted into furfural, whereby same liquor, as discharged from heat exchanger 6, will contain 10-20 grams of furfural per liter. Such a liquor is then sent to thermocompression concentrator 8, wherein it is concentrated up to a dry matter contents of 520-560 grams per liter. All furfural present in the liquor is passed in the vapours that are evolved during such a concentration, whereby a condensed liquid with a furfural contents of 2-4 percent is obtained. Such a liquid is then sent to distillation column 9, wherein the furfural is distillated off. The concentrated liquor as discharged from concentrator 8, and showing a dry matter contents of 520-560 grams per liter, can be directly utilized as a low grade fuel.

While the invention has been described with some detail, it is to be understood that the description is for the purpose of illustration only and is not definitive of the limits of the inventive idea, as changes may be made therein as fall within the spirit and the scope of the attached claim.

What I claim is:

In a process for converting waste bisulfite liquor to furfural and a low grade fuel by evaporation and cyclization in a multiple stage concentrator, that improvement comprising concentrating said liquor to increase its solids content to about twice the solids content of the starting liquor in a first concentration stage at a temperature of ISO- C. and under superatmospheric pressure, simultaneously cyclizing the pentoses and hexoses in said first stage to form furfural, said furfural evolving as vapor with the water of the liquor, raising the temperature and pressure to about to C. in a second stage of concentration and cyclization, cooling said furfural to about 120-130 C. in a heat exchanger and returning the heat from said heat exchanger to said first stage whereby substantially complete conversion of said pentoses and heXoses into furfural is obtained to provide a concentration of at least 10 to 20 grams per liter and to provide a depleted liquor containing at least 520 grams per liter of solids which is suitable as a low grade fuel, said recovered furfural after condensation being distilled to recover substantially pure furfural.

References Cited in the file of this patent UNITED STATES PATENTS 2,463,000 Sevon Mar. 1, 1949 FOREIGN PATENTS 422,330 Italy June 13, 1943 742,147 Germany Nov. 23, 1943 OTHER REFERENCES Perry: Chem. Engineers Handbook (3d ed., 1950), pp. 503, 508-10, 519.

Chem. Engineering Progress, vol. 44, No. 9, September 1948, pp. 669-74. 

